Electrical stimulation of an anatomical region. e.g., deep brain stimulation (DBS), such as of the thalamus or basal ganglia, is a clinical technique for the treatment of disorders such as essential tremor, Parkinson's disease (PD), and other physiological disorders. DBS may also be useful for traumatic brain injury and stroke. Pilot studies have also begun to examine the utility of DBS for treating dystonia, epilepsy, and obsessive-compulsive disorder.
A stimulation procedure, such as DBS, typically involves first obtaining preoperative images, e.g., of the patient's brain, such as by using a computed tomography (CT) scanner device, a magnetic resonance imaging (MRI) device, or any other imaging modality. This sometimes involves first affixing to the patient's skull spherical or other fiducial markers that are visible on the images produced by the imaging modality. The fiducial markers help register the preoperative images to the actual physical position of the patient in the operating room during the later surgical procedure.
After the preoperative images are acquired by the imaging modality, they are then loaded onto an image-guided surgical (IGS) workstation, and, using the preoperative images displayed on the IGS workstation, a neurosurgeon can select a target region. e.g., within the brain, an entry point. e.g., on the patient's skull, and a desired trajectory between the entry point and the target region. The entry point and trajectory are typically carefully selected to avoid intersecting or otherwise damaging certain nearby critical structures or vasculature. e.g., of the brain.
In the operating room, the physician marks the entry point on the patient's skull, drills a burr hole at that location, and affixes a trajectory guide device about the burr hole. The trajectory guide device includes a bore that can be aimed to obtain the desired trajectory to the target region. After aiming, the trajectory guide is locked to preserve the aimed trajectory toward the target region. After the aimed trajectory has been locked in using the trajectory guide, a microdrive introducer is used to insert the surgical instrument along the trajectory toward the target region. e.g., of the brain. The surgical instrument may include, among other things, a recording electrode leadwire, for recording intrinsic electrical signals. e.g., of the brain; a stimulation electrode leadwire, for providing electrical energy to the target region. e.g., of the brain; or associated auxiliary guidewires or guide catheters for steering a primary instrument toward the target region, e.g., of the brain.
The stimulation electrode leadwire, which typically includes multiple closely-spaced electrically independent stimulation electrode contacts, is then introduced to deliver the therapeutic stimulation to the target region, e.g., of the brain. The stimulation electrode leadwire is then immobilized, such as by using an instrument immobilization device located at the burr hole entry. e.g., in the patient's skull, in order for the DBS therapy to be subsequently performed.
The subthalamic nucleus (STN) represents the most common target for DBS technology. Clinically effective STN DBS for PD has typically used electrode contacts in the anterior-dorsal STN. However. STN DBS exhibits a low threshold for certain undesirable side effects, such as tetanic muscle contraction, speech disturbance and ocular deviation. Highly anisotropic fiber tracks are located about the STN. Such nerve tracks exhibit high electrical conductivity in a particular direction. Activation of these tracks has been implicated in many of the DBS side effects. However, there exists a limited understanding of the neural response to DBS. The three-dimensional (3-D) tissue medium near the DBS electrode typically includes both inhomogeneous and anisotropic characteristics. Such complexity makes it difficult to predict the particular volume of tissue influenced by DBS.
After the immobilization of the stimulation electrode leadwire, the actual stimulation therapy is often not initiated until after a time period of about two-weeks to one month has elapsed. This is due primarily to the acute reaction of the brain tissue to the introduced electrode leadwire (e.g., the formation of adjacent scar tissue), and stabilization of the patient's disease symptoms. At that time, a particular one or more of the stimulation electrode contacts is selected for delivering the therapeutic stimulation, and other stimulation parameters are adjusted to achieve an acceptable level of therapeutic benefit.
A system and method may estimate stimulation volumes, and display models of a patient anatomy and/or a stimulation leadwire, via which to graphically identify the estimated stimulation volumes and how they interact with various regions of the patient anatomy, for example, as described in U.S. patent application Ser. No. 12/454,330, filed May 15, 2009 (“the '330 application”), U.S. patent application Ser. No. 12/454,312, filed May 15, 2009 (“the '312 application”), U.S. patent application Ser. No. 12/454,340, filed May 15, 2009 (“the '340 application”), U.S. patent application Ser. No. 12/454,343, filed May 15, 2009 (“the '343 application”), and U.S. patent application Ser. No. 12/454,314, filed May 15, 2009 (“the '314 application”), the content of each of which is hereby incorporated herein by reference in its entirety.